1. Field of Invention
A method, system, device, and computer program product for providing backup battery power to an Ethernet power distribution system.
2. Discussion of the Background
The IEEE 802.3af standard (the 802.3af standard), the entire contents of which are incorporated herein by reference, was approved on Jun. 12, 2003 by the Institute of Electrical and Electronic Engineers (IEEE). The 802.3af standard defines the specifications to deliver power over standard Ethernet cables. The following issues are addressed by the standard:                Legacy Installation—Power over Ethernet ensures safe delivery of power to existing legacy devices as well as power-enabled terminals.        Preservation of Cabling Infrastructure—PoE avoids altering existing wiring and does not damage cabling infrastructure already in place.        Data Integrity—Power delivery over Ethernet cables does not cause data degradation or loss of data integrity.        
When the Ethernet was created, the equipment to be linked drew 50 to a few hundred watts, far too much power to think of sending over data lines. But in the past few years, more and more nontraditional devices have been showing up on networks that require much less power—principally wireless LAN access points and Internet protocol (IP) telephones. One of the main benefits of the new 802.3af standard permitting a networked device's power supply to be carried over its data lines is that now organizations installing or extending an Ethernet LAN can do so without the expense of calling in an electrician and running 120-V AC lines.
The 802.3af standard defines two types of basic devices: a powered device (PD), like an IP phone, and power sourcing equipment (PSE), like a Mid-span Power Hub or Powered Ethernet Switch.
According to the standard, the PSE constantly probes the network with a very-low-voltage and -current signal, and when it detects a valid signature (called a PD detection signature), the PSE applies power to the PD via the network. The power supplied is 48 Vdc nominal, 15.4 W max at the output port, over unshielded twisted-pair wiring. It works with existing cable plant, including Category 3, 5, 5e or 6; horizontal and patch cables; patch-panels; outlets; and connecting hardware, without requiring modification.
The current delivered to each node is limited to 350 milliamps. The total amount of continuous power that can be delivered to each node, taking into account some power loss over the cable run, is 12.95 watts. IP phones and wireless LAN access points typically consume 3.5 to 10 watts.
Additionally, the IEEE is currently working to extend the scope of power over Ethernet by increasing the amount of power that can be delivered via the network. This effort is commonly referred to as PoE Plus.
Power is carried on two wire pairs, to comply with safety standards and existing cable limitations. The 802.3af standard power sourcing equipment contains a detection mechanism to prevent sending power to noncompliant devices. Only terminals that present a valid Power over Ethernet signature will receive power, preventing damage to other equipment.
The 802.3af standard defines two types of power sourcing equipment: endpoint and mid-span. Endpoint refers to an Ethernet switch with embedded Power over Ethernet technology. These new switches deliver data and power over the same wiring pairs—transmission pairs 1/2 and 3/6 or data over the standard transmission pairs and power over the spare pair. Mid-span devices resemble patch panels and typically have between six and 24 channels. They are placed between legacy switches and the powered devices. Each of the mid-span's ports has an RJ-45 data input connector and a data/power RJ-45 output connector. Mid-span devices utilize the unused wire pairs 4/5 and 7/8 to carry power, while data runs on the other wire pairs.
Traditionally, network devices, such as IP phones, wireless LAN access points, laptop computers and Web cameras, have required both a network connection and an AC power connection. Given the increasing number of LAN devices in office environments, wiring AC connections for each of them is a costly task. The 802.3af standard eliminates the need for additional AC outlets and the labor cost incurred from contracting electricians to install them.
Additionally, the technology supports a point-to-multipoint power distribution architecture, parallel to the data network. This allows implementers to use a single UPS at the network core to back up multiple scattered devices on the LAN. The 802.3af standard also provides remote access and management via SNMP or Web-based control.
Power over Ethernet is already widely adopted in the market, particularly in the VoIP, wireless LAN and IP Security market where it saves up to 50% of the overall installation costs by eliminating the need to install separate electrical wiring and power outlets. Its other major advantage, particularly for IP telephony and surveillance camera users, is the ability to offer continuous operation even in the event of a power failure by delivering centralized (distributed) battery-backed-up uninterrupted power through a UPS via the local area network (LAN).
In legacy network installations, where the Ethernet switch already exists, where a PoE PSE is being added, the AC input/output UPS is sized to provide backup power for only the Ethernet switch. A typical 24 port Ethernet switch requires only 40 watts of power. A UPS to provide 15-30 minutes of backup power to an Ethernet switch requiring 40 watts of power costs approximately $50.00 to $100.00. The addition of a PoE PSE will require a much larger and more costly UPS. A fully loaded 24 port PSE requires approximately 380 watts of power. A UPS that can provide power to both the PSE and the Ethernet switch, rated at 420 watts for 30 minutes, would cost approximately $500 to $700. Additionally, the backup time requirements for a PoE network-based security system could be even greater because PoE networks are used extensively to provide telephony and security functions.
FIG. 1 is an example of a conventional Power over Ethernet (POE) infrastructure. In a conventional system, an Ethernet switch 1 supplies data to an Ethernet power hub 2. In addition, an uninterruptible power supply (UPS) 3 provides AC power to both the Ethernet switch 1 and the Ethernet power hub 2. Data and power is provided by the Ethernet power hub 2 to various devices such as a VoIP phone 4, network camera, blue tooth access point, and wireless LAN access point.
FIG. 2 provides more detail on the background art, a double conversion AC UPS, which is a standard configuration for professional grade network applications. Here, the UPS 3 includes a power supply 301 that receives AC input power and converts this AC input power to DC power. This DC power charges the internal backup battery pack 305. The DC power is provided to a DC to AC inverter 303 to convert the power back to AC. The AC power provided by the DC to AC inverter 303 is then provided to a power supply 211 within a Power over Ethernet (POE) mid-span hub 21. This AC power is then converted in the AC to DC converter 211, with DC power provided to the Power over Ethernet (POE) circuitry 213. The Power over Ethernet (POE) circuitry 213 also receives Ethernet signals for distribution. The Ethernet signals and the power provided by the AC to DC converter 211 are provided to various devices via the Power over Ethernet (POE) circuitry 213.
As noted above, in a double-conversion conventional AC UPS system there are three power conversions. This is a significantly inefficient system because there is power loss with each power conversion. This results in a considerably reduction in the length of time the AC UPS can provide backup power. Moreover, each power conversion requires a significant amount of complex electronic circuitry. Thus, with each required power conversion, there is a significant increase in cost and decrease in reliability.
The above discussion describes one configuration for an AC UPS, there are additional configurations but they all suffer from the same deficiencies.
What is desired, as recognized by the inventors, is a more efficient, lower cost method of providing backup power in a Power over Ethernet (POE) environment.
The “background” description provided herein is for the purpose of generally presenting the context of the invention. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.